Abstract: :
Purpose:We have previously shown that monitoring expressionof an immediate early gene, c–fos, in a subpopulationof amacrine cells can provide useful information regarding innerretinal circuitry by applying this technique to mice with defectsin the rod visual pathway. However, it is possible that lightinduced c–fos expression can be attributed to opsin containingcells in the inner retina rather than, or in addition to, rodand/or cone photoreceptors. To address this possibility we havestudied the tulp–/– mouse retina which undergoesrapid loss of photoreceptors in the outer retina. Thus, potentialcontributions from ospin containing cells of the inner retinato c–fos activation can be determined by eliminating allphotoreceptors in the outer retina.Methods:After overnight dark adaptation, mice were exposed toa strobe light stimulus presented at 2 Hz for 60 min at 0.4log cd/sec m2. Three wild–type (WT) and 5 tulp–/–mice were studied. Immediately following light exposure eyeswere removed and processed for immunohistochemistry with a c–fosantibody (Santa Cruz Biotechnology). Using light microscopy,c–fos–positive cells were counted in the inner nuclearlayer.Results:In WT mice, the number of inner retinal cells labeledfor c–fos increased with increasing stimulus intensity.However, c–fos expression was not found in the tulp–/–mouse retina or in dark adapted eyes not exposed to the lightstimulus.Conclusions:Under these experimental conditions c–fosactivation is predominantly mediated by rod and cone photoreceptoractivation. These results support the use of c–fos activationas an assay of inner retinal function and, when applied to micelacking particular pathways, to elucidate inner retinal circuitry